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Rasmus Villemoes b234ed6d62 init: move usermodehelper_enable() to populate_rootfs() 
Currently, usermodehelper is enabled right before PID1 starts going
through the initcalls. However, any call of a usermodehelper from a
pure_, core_, postcore_, arch_, subsys_ or fs_ initcall is futile, as
there is no filesystem contents yet.

Up until commit e7cb072eb9 ("init/initramfs.c: do unpacking
asynchronously"), such calls, whether via some request_module(), a
legacy uevent "/sbin/hotplug" notification or something else, would
just fail silently with (presumably) -ENOENT from
kernel_execve(). However, that commit introduced the
wait_for_initramfs() synchronization hook which must be called from
the usermodehelper exec path right before the kernel_execve, in order
that request_module() et al done from *after* rootfs_initcall()
time (i.e. device_ and late_ initcalls) would continue to find a
populated initramfs as they used to.

Any call of wait_for_initramfs() done before the unpacking has been
scheduled (i.e. before rootfs_initcall time) must just return
immediately [and let the caller find an empty file system] in order
not to deadlock the machine. I mistakenly thought, and my limited
testing confirmed, that there were no such calls, so I added a
pr_warn_once() in wait_for_initramfs(). It turns out that one can
indeed hit request_module() as well as kobject_uevent_env() during
those early init calls, leading to a user-visible warning in the
kernel log emitted consistently for certain configurations.

We could just remove the pr_warn_once(), but I think it's better to
postpone enabling the usermodehelper framework until there is at least
some chance of finding the executable. That is also a little more
efficient in that a lot of work done in umh.c will be elided. However,
it does change the error seen by those early callers from -ENOENT to
-EBUSY, so there is a risk of a regression if any caller care about
the exact error value.

Link: https://lkml.kernel.org/r/20210728134638.329060-1-linux@rasmusvillemoes.dk
Fixes: e7cb072eb9 ("init/initramfs.c: do unpacking asynchronously")
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reported-by: Bruno Goncalves <bgoncalv@redhat.com>
Reported-by: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-09-08 11:50:27 -07:00
arch arch: Kconfig: fix spelling mistake "seperate" -> "separate" 2021-09-08 11:50:25 -07:00
block block-5.14-2021-08-27 2021-08-27 16:08:29 -07:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto crypto: drbg - select SHA512 2021-07-16 15:49:31 +08:00
Documentation Documentation/llvm: update IRC location 2021-09-08 11:50:26 -07:00
drivers phy/drivers/stm32: use HZ macros 2021-09-08 11:50:26 -07:00
fs fs/epoll: use a per-cpu counter for user's watches count 2021-09-08 11:50:27 -07:00
include fs/epoll: use a per-cpu counter for user's watches count 2021-09-08 11:50:27 -07:00
init init: move usermodehelper_enable() to populate_rootfs() 2021-09-08 11:50:27 -07:00
ipc Merge branch 'akpm' (patches from Andrew) 2021-07-02 12:08:10 -07:00
kernel fs/epoll: use a per-cpu counter for user's watches count 2021-09-08 11:50:27 -07:00
lib lib/iov_iter.c: fix kernel-doc warnings 2021-09-08 11:50:26 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm percpu: remove export of pcpu_base_addr 2021-09-08 11:50:25 -07:00
net This is a one-liner fix for a serious bug that can cause the server to 2021-08-26 13:26:40 -07:00
samples Networking fixes for 5.14-rc2, including fixes from bpf and netfilter. 2021-07-14 09:24:32 -07:00
scripts checkpatch: improve GIT_COMMIT_ID test 2021-09-08 11:50:27 -07:00
security bpf: Add lockdown check for probe_write_user helper 2021-08-10 10:10:10 +02:00
sound another sound-fixes for 5.14-rc7 2021-08-20 12:31:10 -07:00
tools tools: rename bitmap_alloc() to bitmap_zalloc() 2021-09-08 11:50:27 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Do not leak memory for duplicate debugfs directories 2021-08-04 06:02:03 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap m68k updates for v5.14 2021-06-28 14:01:03 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: update ClangBuiltLinux mailing list 2021-09-08 11:50:26 -07:00
Makefile Linux 5.14 2021-08-29 15:04:50 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.